Semiconductor device manufacturing method

ABSTRACT

A deep isolation trench extending from the main surface of a substrate to a desired depth is formed on the substrate with an insulating film in buried in it to form a through isolation portion. Subsequently, after a MOSFET is formed on the main surface of the substrate, an interlayer insulating film is deposited on the main surface of the substrate. Then, a deep conduction trench extending from the upper surface of the interlayer insulating film to a depth within the thickness of the substrate is formed in a region surrounded by the through isolation potion. Subsequently, a conductive film is buried in the deep conduction trench to form through interconnect portion. Then, after the undersurface of the substrate is ground and polished to an extent not to expose the through isolation portion and the through interconnect portion, wet etching is performed to an extent to expose parts of the lower portion of each of the through isolation portion and the through interconnect portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/064,762, filed on Feb. 25, 2008, issued as U.S. Pat. No.7,705,455, which is entitled to the benefit of and incorporates byreference essential subject matter disclosed in International PatentApplication No. PCT/JP2006 /317283 filed on Aug. 25, 2006 and JapanesePatent Application No. 2005-245564 filed Aug. 26, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device manufacturingmethod, a semiconductor device, and a wafer. More particularly, to athree-dimensional semiconductor device formed by laminating a pluralityof semiconductor devices, a method of manufacturing such athree-dimensional semiconductor device and a wafer.

2. Description of the Related Art

Conventionally, a three-dimensional semiconductor integrated circuitdevice has been known having a structure in which two or more wafers arevertically laminated and are electrically connected therebetween withburied interconnect. For example, Japanese Patent Laid-Open PublicationNo. H11-261000 (hereinafter referred to as a patent document) disclosesa method of manufacturing a three-dimensional semiconductor integratedcircuit device. In this method, firstly, a trench (deep trench) isformed on one of wafers to be laminated. Then, after the inside of thetrench is thermally oxidized, polysilicon is buried in that trench as aconductor to form buried interconnect. Then, the wafer is made thinneruntil the buried interconnect is exposed, and an undersurface bump isformed at the position of each of the buried interconnect on theundersurface of the wafer. Then, after laminating the undersurface bumpsof the wafer and the top-surface bumps formed on the top surface of theother one of the wafers to be laminated, an insulating adhesive isinjected between these two laminated wafers to manufacture athree-dimensional semiconductor integrated circuit device. According tothis manufacturing method, undersurface bumps for connection have to beformed on the undersurface of one of two wafers to be laminated, andtop-surface bumps for connection have to be formed on the top surface ofthe other wafer. After these bumps are connected together, an adhesiveis injected between the two laminated wafers and hardened, therebymanufacturing a three-dimensional semiconductor integrated circuitdevice. Further lamination of layers can be achieved by repeating theseprocesses described above.

Here, a process flow of laminating two wafers, upper and lower, isschematically shown in FIG. 1. For formation of an upper wafer, afterthe wafer is installed, isolation is performed through a normal processto form an element, such as a transistor. Before or after transistorformation, the above-described buried interconnect is formed. In thatcase, when an insulating film and the buried interconnect are formed ata high buried-interconnect forming temperature, which will affecttransistor characteristics (for example, when a deep hole is formedthrough etching and, after the surface is oxidized, polysilicon isburied as the buried interconnect), a buried interconnect is formedbefore transistor formation. On the other hand, when theburied-interconnect forming temperature does not affect the transistorcharacteristics (for example, when a deep hole is formed through etchingand, after an insulating film is deposited, a metal interconnect isburied), a buried interconnect is formed after transistor formation.Then, the following processes are sequentially performed: a multilayerinterconnect process of connecting the elements, wafer thinning process,a process of forming an undersurface insulating film to prevent a shortcircuit between the buried interconnect or undersurface bumps laterformed and a substrate (silicon), and a process of forming undersurfacebumps for connecting buried interconnect of the upper wafer and thelower wafer.

Next, the other one (lower wafer) of the wafers to be laminated isformed by performing processes similar to those for the upper waferdescribed above until the multilayer interconnect process. That is, theprocesses are approximately similar to those for the upper wafer exceptthe process of making the wafer thinner, the process of forming anundersurface insulating film, and the process of forming undersurfacebumps. However, for the last wafer formed to be laminated, the processof forming a buried interconnect may be omitted. On the top surface ofthe lower wafer, bumps are formed for connection to the buriedinterconnect of the upper wafer. Then, position alignment is performedbetween the upper and lower wafers (alignment between the laminatedwafers), the upper and lower wafers are attached together and,furthermore, an adhesive is injected between the wafers to increasemechanical strength of the device.

Meanwhile, when the technology disclosed in the above patent document isused, after a buried interconnect is formed, the wafer is made thinneruntil the buried interconnect is exposed, and bumps are formed at theposition of the buried interconnect on the undersurface of the wafer.When making the wafer thinner, for allowing wafer handling, a glassplate serving as a supporting substrate is bonded on the main surface ofthe wafer with a adhesive sheet or its alternative, and then theundersurface of the wafer is grinded or polished by using, for example,a grinding device using a grinding stone or a CMP (Chemical MechanicalPolishing) device using slurry for polishing, to make the wafer thinner.However, at the time of grinding the wafer, buried interconnect materialor silicon ground by the grinding stone may cause the grinding stone tobe clogged. Also, with a long grinding time, the temperature of thegrinding stone is increased to cause the wafer to be burnt and cracked.As such, a problem arises in which the wafer to be made thinner isdamaged. In recent years, the diameter of the wafer has been increasedin view of, for example, increasing the number of chips obtainable fromone wafer to enhance manufacturing yields. However, as the diameter ofthe wafer is increased, it has to take a sufficient amount of time togrind or polish the wafer accordingly. Moreover, in view of ensuringmechanical strength of the wafer, for example, the thickness of thewafer in manufacturing the wafer has to be thicker to some extent. Thisalso increases the time to grind or polish the wafer. Therefore, theproblem as described above becomes more significant.

Furthermore, in the technology disclosed in the above patent document,at the time of forming bumps on the undersurface of the wafer to belaminated, in order to insulate the substrate from the bumps, aninsulating film is formed on the undersurface of the wafer through, forexample, CVD (Chemical Vapor Deposition) or sputtering, after the waferis made thinner. In this case, however, the processing temperature atthe time of forming an insulating film on the undersurface of the waferis important. That is, in this process, there is a problem in which thethin wafer may be cracked due to the buried interconnect material in thewafer or a film stress of the insulating film attached to theundersurface. Moreover, the insulating film is formed on theundersurface of the wafer in a state where, in view of keepingmechanical strength of the thin wafer, the glass supporting substrateused at the time of wafer thinning is kept attached to the main surfaceof the wafer. However, the temperature for attaching the insulating filmformed on the undersurface of the wafer is higher than the allowabletemperature limit of the adhesive sheet for bonding the wafer and theglass substrate. For this reason, a problem arises in which, in theprocess of forming an insulating film on the undersurface of the wafer,the bonding force of the adhesive sheet is decreased to cause the glasssupporting substrate to fall off.

Still further, in the technology disclosed in the above patent document,contact holes have to be formed at positions where bumps are formed onthe undersurface of the wafer for connecting the buried interconnectsand the bumps. These contact holes are small, and alignment of aphotomask for forming these holes is difficult. Moreover, to form bumpson the undersurface of the wafer, cumbersome processes are required,including a series of lithography processing, such as application of aresist, exposure, and development, and etching with a resist patternformed through the lithography processing as a mask. This poses anotherproblem of increasing the manufacturing time.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above problems. Anobject of the present invention is to provide a method capable ofavoiding problems in making a wafer thinner and capable of reducingprocesses for electrical connection between wafers to be laminated.

In order to achieve the above said object, a semiconductor devicemanufacturing method and a semiconductor device according to the presentinvention are configured as follows.

That is, the present invention is directed to a semiconductor devicemanufacturing method of laminating a plurality of wafers andelectrically connecting semiconductor circuit units on chips of thewafers together to obtain a desired semiconductor circuit. In themethod, forming at least one of the plurality of wafers, forming a firsttrench in a main surface of the wafer, and then forming a throughisolation portion by burying a first insulating film in the firsttrench; a process of forming an element on the main surface of thewafers comprising the steps of: forming a second trench within a regionsurrounded by the through isolation portion on the main surface of thewafer, and then forming a through interconnect portion electricallyconnected to a semiconductor circuit unit of another wafer by burying aconductive film in the second trench; and making the wafer thinner to anextent not to reach to the through isolation portion and the throughinterconnect portion from an undersurface of the wafer, and then etchinguntil part of the through isolation portion and the through interconnectportion is exposed.

Also, the present invention is directed to a semiconductor devicemanufacturing method of laminating a plurality of wafers together andelectrically connecting semiconductor circuit units on chips of thewafers together to obtain a desired semiconductor circuit, the methodcomprising the steps of: for a wafer of the wafers that is positioned onan upper side, forming a first trench in a main surface of the waferpositioned on the upper side, and then forming a through isolationportion by burying a first insulating film in the first trench; formingan element on the main surface of the wafer positioned on the upperside; forming a second trench within a region surrounded by the throughisolation portion on the main surface of the wafer positioned on theupper side, and then forming a through interconnect portion electricallyconnected to a semiconductor circuit unit of another wafer by burying aconductive film in the second trench; and exposing parts of the throughisolation portion and the through interconnect portion of anundersurface of the wafer positioned on the upper side, wherein the stepof laminating the plurality of wafers together includes a step ofelectrically connecting the semiconductor circuit units of therespective plurality of wafers by jointing the through interconnectportion exposed from the undersurface of the wafer of the pluralitywafers that is positioned on the upper side and a bump formed on a mainsurface of a wafer of the plurality of wafers that is positioned on alower side, with the through interconnect portion and the bump being incontact with each other.

Furthermore, the present invention is directed to a semiconductor devicein which a desired semiconductor circuit is obtained by laminating aplurality of substrates and electrically connecting semiconductorcircuit units formed on the respective substrates together, wherein asubstrate of the plurality of substrates that is positioned on an upperside has a through interconnect portion penetrating from a main surfaceto an underside of the substrate and a through isolation portion that isdisposed at a position on the main surface of the upper substrate awayfrom the through interconnect portion so as to surround the throughinterconnect portion and penetrate from the main surface through theundersurface of the upper substrate, a substrate of the plurality ofsubstrates that is positioned at a lower side has a bump on a mainsurface of the substrate, the bump being electrically connected to asemiconductor circuit unit formed on the substrate on the lower side,and the semiconductor circuit unit of the substrate on the upper sideand the semiconductor circuit unit of the substrate on the lower sideare electrically connected to each other by jointing the throughinterconnect portion exposed from the undersurface of the substratepositioned on the upper side with the bump of the main surface of thesubstrate positioned on the lower side.

According to the present invention, it is possible to provide a methodcapable of avoiding problems in making a wafer thinner and capable ofreducing processes for electrical connection between wafers to belaminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of a conventional manufacturing process oflaminating two wafers, that is, upper and lower wafers;

FIG. 2 is a flow diagram of a semiconductor device manufacturing processaccording to an embodiment of the present invention;

FIG. 3 is a cross-section view of main parts of an upper wafer during amanufacturing process;

FIG. 4 is a cross-section view of the main parts of the upper waferduring the manufacturing process continued from FIG. 3;

FIG. 5 is a plan view of the main parts of the upper wafer during themanufacturing process continued from FIG. 4;

FIG. 6 is a cross-section view along an A-A line in FIG. 5;

FIG. 7 is a cross-section view of the main parts of the upper waferduring the manufacturing process continued from FIGS. 5 and 6;

FIG. 8 is a cross-section view of the main parts of the upper waferduring the manufacturing process continued from FIG. 7;

FIG. 9 is a plan view of the main parts of the upper wafer during themanufacturing process continued from FIG. 8;

FIG. 10 is a cross-section view along an A-A line in FIG. 9;

FIG. 11 is a cross-section view of the main parts of the upper waferduring the manufacturing process continued from FIGS. 9 and 10;

FIG. 12 is a cross-section view of the main parts of the upper waferduring the manufacturing process continued from FIG. 11;

FIG. 13 is a cross-section view of the main parts of the upper waferafter first and second thinning processes continued from FIG. 12;

FIG. 14 is a cross-section view of the main parts of the upper waferafter a third thinning process continued from FIG. 13;

FIG. 15 is a cross-section view of main parts of a lower wafer at astage of a bump forming process;

FIG. 16 is a cross-section view of the main parts of the lower waferduring the manufacturing process continued from FIG. 15;

FIG. 17 is a cross-section view of main parts during a process oflaminating the upper and lower wafers;

FIG. 18 is a cross-section view of the main parts during the process oflaminating the upper and lower wafers continued from FIG. 17;

FIG. 19 is a cross-section view of the main parts during the process oflaminating the upper and lower wafers continued from FIG. 18; and

FIG. 20 is a cross-section view of a semiconductor device having athree-dimensional structure according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments (examples) of the present invention are describedbelow along a flow diagram of FIG. 2 with reference to FIGS. 3 to 19.

A method of manufacturing an upper wafer is first described. FIG. 3 is across-section view of main parts of an upper wafer (a wafer of theuppermost layer) 1WA during a manufacturing process. First, the wafer1WA is prepared (step 100A in FIG. 2). The wafer 1WA is formed of, forexample, a thin plate in approximately circular shape. This wafer 1WAforms a substrate 1SA, which is made of, for example, an n-type orp-type single crystal silicon (Si), and has a main surface and anundersurface those are opposite to each other in a thickness direction.Then, trench-shaped isolation portions 2 for isolation are formed on themain surface of the substrate 1SA (that is, the main surface of thewafer 1WA) (step 101A in FIG. 2). Each of the trench-shaped isolationportions 2 is formed by forming an isolation trench 2 a on the mainsurface of the substrate 1SA and then burying an insulation film 2 b,such as, for example, silicon oxide (SiO₂), in the isolation trench 2 a.With these isolation portions 2, an active region of the main surface ofthe substrate 1SA is defined. Here, an insulating film 3 on the mainsurface of the active region of the substrate 1SA is made of, forexample, silicon oxide formed through, for example, thermal oxidation.

Next, a through isolation portion is formed on the substrate 1SA. First,a resist film is applied on the main surface of the substrate 1SAthrough, for example, spin coating, and is then exposed and developed(such a series of processes of applying a resist, exposure, anddevelopment is referred to as lithography processing). With this, aresist pattern RA is formed on the main surface of the substrate 1SA.The resist pattern RA is formed so as to expose regions where throughisolation portions are to be formed and so as to cover the otherregions.

Then, with this resist pattern RA as an etching mask, the insulatingfilm 3 and the substrate 1SA exposed from the etching mask are etched,thereby forming deep isolation trenches (first trenches) 5 a on thesubstrate 1SA, as shown in FIG. 4. FIG. 4 is a cross-section view of themain parts of the upper wafer after the deep isolation trenches 5 a areformed. These deep isolation trenches 5 a extend from the main surfaceof the substrate 1SA along a direction (vertically) crossing the mainsurface (that is, a thickness direction of the substrate 1SA), and areterminated at a position (first position) deeper than the isolationtrenches 2 a for isolation.

Then, after the resist pattern RA is removed, thermal oxidation isperformed on the substrate 1SA, thereby forming an insulating film madeof, for example, silicon oxide, on inner surfaces (inner side surfacesand bottom surfaces) of each of the deep isolation trenches 5 a.Furthermore, an insulating film made of, for example, silicon oxide orLow-k (low dielectric constant) material, is deposited on the mainsurface of the substrate 1SA through, for example, CVD (Chemical VaporDeposition), to be buried in each of the deep isolation trenches 5 a.

Then, superfluous portions of the insulating film outside of the deepisolation trenches 5 a are removed through an etch-back process usinganisotropic dry etching or Chemical Mechanical Polishing (CMP). Withthis, as shown in FIGS. 5 and 6, through isolation portions 5 are formed(step 102A in FIG. 2).

FIG. 5 is a plan view of the main parts of the upper wafer 1WA duringthe manufacturing process continued from FIG. 4, and FIG. 6 is across-section view along an A-A line in FIG. 5. Although FIG. 5 is aplan view, this drawing includes hatching on the through isolationportions 5 for ease of viewing. Viewed from the top, the throughisolation portions 5 are each formed in a rectangular frame shape, forexample. The through isolation portion 5 is formed by burying aninsulating film 5 b (first insulating film) formed in theabove-described manner in the deep isolation trench 5 a. The depth ofthe through isolation portion 5 (that is, the depth of the deepisolation trench 5 a) may be deeper than the depth of a throughinterconnect portion, which will be described further below, or may beequal to or shallower than that. For example, when the dimension of agap between wafers vertically laminated is controlled with the depth ofthe through isolation portion 5, the depth of the through isolationportion 5 may be deeper than that of the through interconnect portion.Furthermore, when the dimension of the gap is controlled with the depthof the through interconnect portion, the depth of the through isolationportion 5 may be shallower than the depth of the through interconnectportion. Still further, when the dimension of the gap is controlled withanother factor, the depth of the through isolation portion 5 may beequal to that of the through interconnect portion.

Next, after the insulating film 3 is removed, as shown in FIG. 7, anelement, such as, for example, a MOSFET (Metal Oxide Semiconductor FieldEffect Transistor) 6, is formed in an active region surrounded by thetrench-shaped isolation portions 2 of the substrate 1SA (step 103A inFIG. 2). FIG. 7 is a cross-section view of the main parts of the upperwafer 1WA during the manufacturing process continued from FIGS. 5 and 6.The MOSFET 6 has semiconductor regions for source and drain 6 a, a gateinsulating film 6 b, and a gate electrode 6 c. The semiconductor regionsfor source and drain 6 a are formed by adding desired impurities (forexample, phosphorus (P) or arsenic (As) in the case of an n-channelMOSFET 6, and boron (B) in the case of a p-channel MOSFET 6) to thesubstrate 1SA. The gate insulating film 6 b is made of, for example,silicon oxide, and is formed on the main surface of the substrate 1SA.The gate electrode 6 c is made of, for example, low-resistantpolysilicon, and is formed on the gate insulating film 6 b. Here, aninsulating film 7 on the main surface of an active region of thesubstrate 1SA is formed of, for example, an insulating film made ofsilicon oxide.

Here, when the through isolation portions 5 are formed after the MOSFET6 is formed, at the time of thermal oxidation for forming the insulatingfilm 5 b of each through isolation portion 5, impurities in thesubstrate 1SA (the semiconductor regions for source and drain 6 a and achannel formation region under the gate electrode 6 c) may be diffusedagain. This may result in variations in electrical characteristics, suchas a threshold voltage of the MOSFET 6. By contrast, in the presentembodiment, the MOSFET 6 is formed after forming the through isolationportions 5. Therefore, it is possible to avoid variations in electricalcharacteristics of the MOSFET 6 due to a high processing temperature atthe time of forming the through isolation portions 5. Thus, reliabilityof the semiconductor device can be increased. Here, in place of theMOSFET 6, another active element, for example, a bipolar transistor or adiode, may be formed. Also, in place of the MOSFET 6, a passive element,such as, for example, a resistor (a diffused resistor or a polysiliconresistor), a capacitor, and an inductor, may be formed.

Next, the through interconnect portions are formed. First, an insulatingfilm made of, for example, silicon oxide, is deposited on the mainsurface of the substrate 1SA through, for example, CVD, and then theupper surface of the insulating film is planarized, thereby forming aninterlayer insulating film (second insulating film) 8 a. The MOSFET 6,the through isolation portions 5, the trench-shaped isolation portions 2and others are covered by the interlayer insulating film 8 a. Then, aresist pattern RB is formed on the interlayer insulating film 8 athrough the above-described lithography processing. The resist patternRB is formed so as to expose regions where the through interconnectportions to be formed and so as to cover the other regions. Then, withthis resist pattern RB as an etching mask, the interlayer insulatingfilm 8 a, the insulating film 7, and the substrate 1SA exposed from theetching mask are etched, thereby forming deep conduction trenches(second trenches) 9 a in the substrate 1SA, as shown in FIG. 8. FIG. 8is a cross-section view of the main parts of the upper wafer 1WA afterthe deep conduction trenches 9 a are formed. These deep conductiontrenches 9 a extend from the upper surface of the interlayer insulatingfilm 8 a along a direction (vertically) crossing the upper surface (thatis, a thickness direction of the substrate 1SA), and are terminated at aposition (second position) deeper than the isolation trenches 2 a forisolation. The depth of the deep conduction trenches 9 a is to be asdescribed in the description about the depth of the through isolationportion 5. Here, by way of example, the depth of the deep conductiontrench 9 a (second position) is shallower than the depth of the deepisolation trench 5 a (first position).

Then, after the resist pattern RB is removed, a barrier conductive filmmade of, for example, titanium nitride, is deposited on the main surfaceof the substrate 1SA through, for example, sputtering. Furthermore, amain conductive film made of, for example, tungsten, is depositedthrough, for example, CVD, to be buried in each of the deep conductiontrenches 9 a. This barrier conductive film is formed so as to cover theside and bottom surface of the main conductive film, and is in directcontact with the substrate 1SA through inner surfaces (inner sidesurfaces and bottom surfaces) of each of the deep conduction trenches 9a. The thickness of the barrier conductive film is thinner than thethickness of the main conductive film.

Then, the main conductive film and the barrier conductive film arepolished through, for example, CMP. With this, as shown in FIGS. 9 and10, superfluous portions of the main conductive film and the barrierconductive film outside of the deep conduction trenches 9 a are removed,thereby causing the main conductive film and the barrier conductive filmto be left only in the deep conduction trenches 9 a. With this, thethrough interconnect portions 9 are formed in the deep conductiontrenches 9 a (step 104A in FIG. 2).

FIG. 9 is a plan view of the main parts of the upper wafer 1WA duringthe manufacturing process continued from FIG. 8, and FIG. 10 is across-section view along an A-A line in FIG. 9. Although FIG. 9 is aplan view, this drawing includes hatching on the through isolationportions 5 and the through interconnect portions 9 for ease of viewing.Viewed from the top, the through interconnect portions 9 are each formedin an elongated rectangular shape, for example. Each of the throughinterconnect portions 9 is placed in the frame of the through isolationportion 5 in a state of being separated from the through isolationportion 5. That is, the through interconnect portion 9 is placed so asto be surrounded by the through isolation portion 5 placed at a desireddistance away from the through interconnect portion 9.

The through interconnect portion 9 is formed by burying a conductivefilm (the barrier conductive film and the main conductive film) 9 b inthe deep conduction film 9 a. That is, since the through interconnectportion 9 is made of metal, in comparison with the case where thethrough interconnect portion 9 is made of low-resistant polysilicon,electric resistance of the through interconnect portion 9 can besignificantly reduced. In particular, in the present embodiment, sincethe shape of the through interconnect portion 9 viewed from the top is alarge rectangle, the deep conduction trench 9 a can be easily processed,and a large volume of the through interconnect portion 9 can be ensured,thereby making it possible to further reduce electric resistance of thethrough interconnect portion 9. Also, the upper surface of each of thethrough interconnect portions 9 coincides with the upper surface of theinterlayer insulating film 8 a. With this, flatness of the upper surfaceof the interlayer insulating film 8 a can be ensured.

Furthermore, if the through isolation portion 5 and the throughinterconnect portion 9 are integrated together, these portions have tobe formed in the same process. Therefore, when the through isolationportions 5 are formed before element formation in order to avoidvariations in element characteristics as described above, the throughinterconnect portions 9 also have to be formed before element formation.However, if the through interconnect portions 9 are formed beforeelement formation, there is a problem of high possibly of causingdeterioration in element characteristics and metal contamination. To getaround this problem, in the present embodiment, the through isolationportions 5 and the through interconnect portions 9 can be separatelyformed, and the through interconnect portions 9 can be formed after theMISFET 6 and the interlayer insulating film 8 a are formed. Therefore,the possibility of causing deterioration in element characteristics andmetal contamination can be further reduced. Thus, electriccharacteristics of the element can be improved.

The number of through interconnect portions 9 in each of the throughisolation portions 5 is not restricted to one. For example, a pluralityof through interconnect portions 9 may be placed in the frame of onethrough isolation portion 5. Also, the planer shape of the throughisolation portion 5 is not restricted to that shown in the example ofFIG. 9. For example, another shape, such as a square, may suffice.

Next, as shown in FIG. 11, a multilayer interconnect layer is formed onthe main surface of the substrate 1SA through a normal interconnectformation method in a semiconductor device (step 105A in FIG. 2). FIG.11 is a cross-section view of the main parts of the upper wafer 1WAduring the manufacturing process continued from FIGS. 9 and 10.Reference numerals 8 b, 8 c, and 8 d denote interlayer insulating films,a reference numeral 10 denotes a surface protective film, referencenumerals 15 a, 15 b, and 15 c denote wires, reference numerals 16 a, 16b, 16 c, and 16 d denote plugs.

The interlayer insulating films 8 b, 8 c, and 8 d are made of, forexample, silicon oxide. The wires 15 a to 15 c and the plugs 16 a to 16d are made of metal, such as tungsten (W), aluminum (Al), or copper(Cu). The wire 15 a on a first layer is electrically connected to thesemiconductor region for source and drain 6 a and the gate electrode 6 cof the MOSFET 6 through the plug 16 a, and also electrically connectedto the through interconnect portion 9 through the plug 16 b. The surfaceprotective film 10 is formed of, for example, a single silicon oxidefilm, or a laminated film of silicon oxide and a silicon nitride filmdeposited thereon. Part of this surface protective film 10 has formedthereon openings 17 from each of which a part of the wire 15 c on athird layer is exposed. The portion of each wire 15 c exposed from theopening 17 when viewed from the top is denoted as a bonding pad(hereinafter referred to as a pad) BP, although this portion seemsidentical to other portions of the wire 15 c in the drawing. Here,although not shown in FIG. 11, after the process of forming a multilayerinterconnect layer, bumps may be formed so as to be connected to thepads BP on the main surface of the wafer 1WA.

Next, as shown in FIG. 12, a glass supporting substrate 21 is laminatedon the main surface of the wafer 1WA interposing an adhesive sheet 20therebetween. FIG. 12 is a cross-section view of the main parts of theupper wafer 1WA during the manufacturing process continued from FIG. 11.As such, with the glass supporting substrate 21 being laminated on themain surface of the wafer 1WA, handling of the wafer 1WA can bestabilized. Also, mechanical strength of the thin wafer 1WA after thelater process of making the film thinner can be ensured.

Next, the wafer 1WA is made thinner (step 107 in FIG. 2). The process ofmaking the wafer 1WA thinner according to the present embodimentincludes a first thinning process, a second thinning process, and athird thinning process as follows.

First, in the first thinning process, as shown in FIG. 13, with theglass supporting substrate 21 being attached to the main surface of thewafer 1WA, the undersurface of the wafer 1WA (that is, the undersurfaceof the substrate 1SA) is ground so as to have a desired thickness. Also,after this grinding, as the second thinning process, a polishing processmay be performed on the undersurface of the wafer 1WA. This polishingprocess is a thinning process with mechanical and chemical elements, forexample, CMP. With this, a damaged layer on the undersurface of thewafer 1WA through the grinding process can be removed, and also theundersurface of the wafer 1WA can be smoothed, thereby making chemicalstability in the undersurface of the wafer 1WA uniform. Therefore, inetching to be performed later on the undersurface portion of the wafer1WA, it is possible to ensure a uniform amount of etching removal in athickness direction of the wafer 1WA on the entire undersurface of thewafer 1WA. FIG. 13 is a cross-section view of the main parts of theupper wafer 1WA after such first and second thinning processes. A dottedline represents the substrate 1SA before the first thinning process. Amain object of these first and second thinning processes is to reducetime for a wafer thinning process. The first thinning process is athinning process with a mechanical element typified by grinding, whilstthe second thinning process is a thinning process with mechanical andchemical elements typified by polishing. These first and second thinningprocesses end in the state where the through isolation portions 5 andthe through interconnect portions 9 are not reached (that is, thethrough isolation portions 5 and the through interconnect portions 9 arenot exposed from the undersurface of the wafer 1WA).

Then, in the third thinning process, as shown in FIG. 14, with the glasssupporting substrate 21 being attached to the main surface of the wafer1WA, the undersurface of the wafer 1WA is soaked into a chemicalsolution and is then etched (wet etching), thereby exposing part of thethrough isolation portions 5 and the through interconnect portions 9from the undersurface of the wafer 1WA. FIG. 14 is a cross-section viewof the main parts of the upper wafer 1WA after the third thinningprocess. A dotted line represents the substrate 1SA before the thirdthinning process. The third thinning process is a thinning process witha chemical element typified by wet etching. A main object of the thirdthinning process is to prevent burns and damages of the wafer 1WA at thetime of thinning process. Here, part of a lower portion of each of thethrough interconnect portions 9 protrudes from the undersurface of thewafer 1WA for a predetermined length. The protruding length of eachthrough interconnect portion 9 from the undersurface of the wafer 1WA isdetermined so as to avoid inconveniences in consideration of laterprocesses. With this process, the through interconnect portions 9 areisolated from the substrate 1SA by the through isolation portions 5 in aside-surface direction. The lower portion of each through interconnectportion 9 is isolated from the substrate 1SA with the throughinterconnect portion 9 being exposed. Thus, the through interconnectportions are fully isolated from the substrate 1SA. Here at this state,the deep isolation trenches 5 a and the deep conduction trenches 9 aserve as holes penetrating through the main surface and the undersurfaceof the substrate 1SA. Also, in the above example, in the process ofthinning the wafer 1WA, the case of sequentially performing the firstthinning process (grinding) and the third thinning process (etching) andthe case of sequentially performing the first thinning process(grinding), the second thinning process (polishing), and the thirdthinning process (etching) have been described. Alternatively, forexample, by sequentially performing the second thinning process(polishing) and the third thinning process (etching), the wafer 1WA canalso be made thinner.

According to the above-described thinning processes, with the combineduse with wet etching, burns and damages of the wafer 1WA occur in thecase of making the wafer 1WA thinner through only grinding and polishingcan be suppressed or prevented. In particular, when the wafer 1WA ismade thinner only through grinding and polishing, a large diameter ofthe wafer 1WA is required. Larger the wafer 1WA is, longer the time forgrinding is required, resulting in an increase in wafer temperature.Also, when a hard material is used for the through interconnect potions9, the through interconnect material and silicon ground at the time ofgrinding may cause the grinding stone to be clogged and may increase thewafer temperature. By contrast, as in the present embodiment, bycombined use with wet etching in the process of thinning the wafer 1WA,it is possible to avoid a significant increase in wafer temperature inthe process of thinning the wafer 1WA even if the diameter of the wafer1WA is large and a hard material is used as for the through interconnectportions 9. Therefore, burns and damages of the wafer 1WA can besuppressed or prevented. On the other hand, in the thinning processes,the wafer 1WA is made thinner not only through etching but also with thecombined use with grinding and polishing, the thinning process time canbe reduced compared with the case of removing the undersurface portionof the wafer 1WA only through etching.

In this manner, the process of manufacturing the upper wafer 1WA ends.As such, in the present embodiment, no insulating film is deposited onthe undersurface of the wafer 1WA or no bump forming process isrequired. Therefore, the following effects can be achieved.

First, since a process of depositing an insulating film on theundersurface of the wafer 1WA is not performed, problems due to theprocessing temperature at the time of depositing an insulating film canbe avoided. That is, a problem can be avoided in which the thin wafer iscracked due to the buried interconnect material in the wafer or a filmstress of the insulating film. Also, another problem can be avoided inwhich, in the process of depositing an insulating film on theundersurface of the wafer, the adhesion force of the adhesive sheet 20for the glass supporting substrate 21 is decreased to cause the glasssupporting substrate 21 to fall off. Therefore, since there is notemperature restriction at the time of selecting a material of theadhesive sheet 20, the range of selection for the adhesive sheet 20 canbe widened.

Second, since a process of forming bumps on the undersurface of thewafer 1WA is not performed, problems in bump formation can be avoided.That is, it is possible to eliminate a process of forming a smallcontact hole on the insulating film on the undersurface of the wafer ora process of forming bumps on the undersurface of the wafer, therebyeliminating, for example, lithography processing accompanied with manydifficult processes. Therefore, the semiconductor device manufacturingprocess can be simplified, and the manufacturing time can be reduced.Also, reliability and yields of the semiconductor devices can beimproved.

Next, a process of manufacturing a lower wafer is described. Here, aprocess of manufacturing, as a lower wafer, a wafer of the lowermostlayer with its undersurface not supposed to be laminated with anotherwafer is described. This process of manufacturing a lower wafer is, asshown in the right side of FIG. 2, approximately similar to the processof manufacturing the upper wafer 1WA shown in the left side of FIG. 2.That is, wafer preparation (step 100B), isolation portion formation(step 101B), element formation (step 103B), multilayer interconnectlayer formation (step 105B), and bump formation on the main surface ofthe wafer (step 106B) are sequentially performed. Here, what aredifferent are a bump formation process (step 106B) performed after aprocess of forming a multilayer interconnect layer (step 105B) and forthe lowermost wafer, none of wafer thinning process, process of formingthrough isolation portions (step 102B) and process of forming throughinterconnect portions (step 104B) is performed.

FIG. 15 is a cross-section view of main parts of a lower wafer (a waferof the lowermost layer) 1WB at a stage of a bump forming process 106Bafter steps from 100B to 105B in FIG. 2. The configuration of the wafer1WB is approximately similar to that of the upper wafer 1WA shown inFIG. 11 after the step 105A. From the undersurface of the wafer 1WB(that is, the undersurface of the substrate 1SB), the through isolationportions 5 and the through interconnect portions 9 are not exposed.

Here, first, a conductive film is deposited through, for example,sputtering, on the main surface of the wafer 1WB after the step ofmanufacturing a multilayer interconnect layer 105B, and is thenpatterned by using lithography processing and etching, thereby formingunder bump conductive patterns 25. Each of these under bump conductivepatterns 25 is electrically connected to the pad BP through the opening17. Then, as shown in FIG. 16, a bump 26 is formed on each under bumpconductive pattern 25 through, for example, lift-off method,electrolytic plating, printing, or ball drop. As a result, the bump 26is electrically connected to the uppermost interconnect layer 15 c ofthe lower wafer 1WB. FIG. 16 is a cross-section view of the main partsof the lower wafer 1WB during the manufacturing process continued fromFIG. 15. The main surface of the lower wafer 1WB has placed thereon aplurality of bumps 26 in a state of protrusion. In this manner, theprocess of manufacturing the lower wafer 1WB ends. The lower wafer 1WBhas no insulating film deposited or no bump formed on the undersurface,and therefore the same effects as described above for the upper wafer1WA can be achieved.

Next, a process of laminating the upper and lower wafers 1WA and 1WBmanufactured in the manner described above is described with referenceto FIGS. 17 to 19. FIGS. 17 to 19 are cross-section views of main partsduring a process of laminating the upper and lower wafers 1WA and 1WB.

First, as shown in FIG. 17, after the lower wafer 1WB is fixed, theupper wafer 1WA is placed above the main surface of the lower wafer 1WBwith the undersurface of the upper wafer 1WA facing the main surface ofthe lower wafer 1WB. At this time, the state is such that the glasssupporting substrate 21 is laminated on the main surface of the upperwafer 1WA. With this, the thin wafer 1 WA can be handled as beingstabilized. Also, mechanical strength of the wafer 1WA can also beensured. Therefore, the wafer 1WA can be handled without causing, forexample, cracking, chipping, or warpage, on the wafer 1WA at the time ofcarrying the wafer 1WA.

Then, relative positions of the lower wafer 1WB and the upper wafer 1WAare aligned with each other. Specifically, the bumps 26 on the mainsurface of the lower wafer 1WB and the through interconnect portions 9on the undersurface of the upper wafer 1WA are aligned with each other(step 201 in FIG. 2). Then, as shown in FIG. 18, facing surfaces of theupper and lower wafers 1WA and 1WB are brought close to each other tostack the upper wafer 1WA on the main surface of the lower wafer 1WB,thereby brining the bumps 26 on the main surface of the lower wafer 1WBand the through interconnect portions 9 on the undersurface of the upperwafer 1WA into contact with each other for electrical connection. Withthis, semiconductor circuit units of the upper and lower wafers 1WA and1WB are electrically connected to each other. Here, each of the bumps 26on the main surface of the lower wafer 1WB is within the frame of thethrough isolation portion 5 surrounding the through interconnect portion9 on the undersurface of the upper wafer 1WA to which the bump 26 isconnected (step 202 in FIG. 2).

Next, an adhesive 30 with insulation properties is injected in a gapbetween the facing surfaces of the upper and lower wafers 1WA and 1WB.With this, mechanical strength between the upper and lower wafers 1WAand 1WB is ensured. Here, an exemplary case is illustrated in which theadhesive 30 gets into even the frames of the through isolation portions5. However, since the adhesive 30 with insulation properties is used,this case does not pose a problem to the characteristics of the device.Also, even in case of the upper and lower wafers 1WA and 1WB are incontact with each other at a thin portion due to crude density of thethrough interconnect portions 9, no inconvenience occurs in devicecharacteristics (step 203 in FIG. 2). Then, as shown in FIG. 19, theglass supporting substrate 21 is delaminated from the main surface ofthe upper wafer 1WA.

After the processes as described above, the laminated wafers 1WA and 1WBare cut into chips. Each of these chips has a three-dimensionalconfiguration such that a plurality of chips are laminated. That is,with semiconductor circuits of the respective chips forming one chipbeing electrically connected each other through the through interconnectportions 9, one desired semiconductor integrated circuit as a whole isformed on each chip.

Next, FIG. 20 is an exemplary cross-section view of main parts of asemiconductor device having a three-dimensional structure formed bylaminating three layers of substrates 1SA, 1SB, and 1SC. Here, anexemplary case is illustrated in which the adhesive 30 injected in a gapbetween the uppermost substrate 1SA and the intermediate substrate 1SCdoes not extend to the inside of the frame surrounded by the throughisolation portion 5.

Here, an example of a process of manufacturing a three-dimensionalsemiconductor device in a multilayer laminated configuration as shown inFIG. 20 is described.

First, in a manner as described with reference to FIGS. 3 to 14, thewafer 1WA of the uppermost layer is prepared. Also, in a manner asdescribed with reference to FIGS. 15 and 16, the wafer WB of thelowermost layer is prepared. Furthermore, through steps from 100B to106B on the right side of FIG. 2, the wafer 1WC of the intermediatelayer is prepared. On this wafer 1WC of the intermediate layer, as withthe wafer 1WA of the uppermost layer, the through isolation portions 5and the through interconnect portions 9 are formed. The wafer 1WC of theintermediate layer is different from the wafer 1WA of the uppermostlayer in that the bumps 26 are formed on the main surface of the wafer1WC of the intermediate layer through a interconnect layer. The bumps 26of the wafer 1WC of the intermediate layer are electrically connected toelements and the through interconnect portions 9 of the wafer 1WC of theintermediate layer through the interconnect layer. Also, the wafer 1WCof the intermediate layer at this state has not yet been subjected tothe first to third thinning processes, and therefore is still thick.

Then, in a manner as described with reference to FIGS. 17 and 18, twowafers 1WA and 1WC are laminated together. At this time, since the wafer1WC of the intermediate layer is still thick, the wafer 1WC can bestably and easily handled. Then, with the glass supporting substrate 21being kept laminated on the main surface of the wafer 1WA of theuppermost layer and further, with the two wafers 1WA and 1WC being keptlaminated, the wafer 1WC of the intermediate layer located lower is madethinner from its undersurface through a thinning process as describedwith reference to FIGS. 13 and 14 (step 107A at the center in FIG. 2).With this, the through isolation portions 5 and the through interconnectportions 9 are exposed (protruded) from the undersurface of the wafer1WC of the intermediate layer located lower. Since the wafer 1WC of theintermediate layer is made thinner with the two wafers 1WA and 1WC beingkept laminated, mechanical strength of the wafer 1WC at the time of thethinning process can be ensured, and also the stability in handling ofthe wafer 1WC can be improved. Thus, thinning the wafer 1WC can befacilitated.

After that, with the glass supporting substrate 21 being kept laminatedon the main surface of the wafer 1WA of the uppermost layer locatedupper and with the two wafers 1WA and 1WC being kept laminated, in amanner as described with reference to FIGS. 17 and 18, the wafer 1WC ofthe intermediate layer located lower and the wafer 1WB of the lowermostlayer are stacked together, and then the adhesive 30 is injected betweenthe wafers 1WC and 1WB for lamination (steps from 201 to 203 at thebottom of the center potion of FIG. 2). Thereafter, the processes arethe same as described above, and are not described herein. When three ormore wafers are laminated, the processes performed on the wafer 1WC ofthe intermediate layer and the wafer lamination process can be repeated.

According to such a wafer lamination method, lamination of a pluralityof wafers can be successively and stably performed, thereby reducing themanufacturing time of three-dimensional semiconductor devices andimproving mass productivity of three-dimensional semiconductor devices.

The present invention can be applied to three-dimensional semiconductordevice manufacturing industries.

While the present invention has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisinvention may be made without departing from the spirit and scope of thepresent invention.

1. A semiconductor device manufacturing method comprising the steps of:forming a first trench in a main surface of the wafer, and then forminga through isolation portion by burying a first insulating film in thefirst trench; forming an element on the main surface of the wafer;forming a second trench within a region surrounded by the throughisolation portion on the main surface of the wafer, and then forming athrough interconnect portion electrically connected to a semiconductorcircuit unit of another wafer by burying a conductive film in the secondtrench; and making the wafer thinner to an extent not to reach to thethrough isolation portion and the through interconnect portion from anundersurface of the wafer, and then etching from the undersurface of thewafer until parts of the through isolation portion and the throughinterconnect portion are exposed.
 2. The semiconductor devicemanufacturing method according to claim 1, wherein the step of formingthe through isolation portion includes a step of forming an insulatingfilm in the first trench through thermal oxidation, and the element isformed after the through isolation portion is formed.
 3. Thesemiconductor device manufacturing method according to claim 1, furthercomprising: a step of forming the element on the main surface of thewafer and then depositing a second insulating film on the main surfaceof the wafer so as to cover the element; a step of forming the secondtrench extending from an upper surface of the second insulating film toa position within a thickness of the wafer; and a step of burying theconductive film in the second trench to form the through interconnectportion.
 4. The semiconductor device manufacturing method according toclaim 1, wherein the conductive film is made of metal.
 5. Thesemiconductor device manufacturing method according to claim 1, whereinthe step of making the wafer thinner to the extent not to reach thethrough isolation portion and the through interconnect portion isperformed through either one of grinding, polishing, and both ofgrinding and polishing.
 6. A semiconductor device manufacturing methodcomprising the steps of: preparing a plurality of wafers; forming asemiconductor circuit unit on each of the plurality of wafers;laminating the plurality of wafers together and electrically connectingthe semiconductor circuit units on the plurality of wafers to eachother; and after the step of laminating the plurality of waferstogether, cutting the plurality of wafers into chips each having athree-dimensional configuration with a plurality of chips being stackedtogether, wherein a step of forming an upper wafer of the plurality ofwafers comprising the steps of: forming a first trench in a main surfaceof the upper wafer, and then forming a through isolation portion byburying a first insulating film in the first trench; forming an elementon the main surface of the upper wafer; forming a second trench within aregion surrounded by the through isolation portion on the main surfaceof the upper wafer, and then forming a through interconnect portionelectrically connected to a semiconductor circuit unit of another waferof the plurality of wafers by burying a conductive film in the secondtrench; and making the upper wafer thinner to an extent not to reach tothe through isolation portion and the through interconnect portion froman undersurface of the upper wafer, and then etching from theundersurface of the upper wafer until parts of the through isolationportion and the through interconnect portion are exposed.
 7. Thesemiconductor device manufacturing method according to claim 6, whereinthe step of making the wafer thinner to the extent not to reach to thethrough isolation portion and the through interconnect portion isperformed through either one of grinding, polishing, and both ofgrinding and polishing.
 8. A semiconductor device manufacturing methodcomprising the steps of: preparing a plurality of wafers; forming asemiconductor circuit unit on each of the plurality of wafers;laminating the plurality of wafers together and electrically connectingthe semiconductor circuit units on the plurality of wafers to eachother; and after the step of laminating the plurality of waferstogether, cutting the plurality of wafers into chips each having athree-dimensional configuration with a plurality of chips being stackedtogether, wherein a step of forming an upper wafer of the plurality ofwafers, the step of forming the upper wafer comprising the steps of:forming a first trench in a main surface of the upper wafer, and thenforming a through isolation portion by burying a first insulating filmin the first trench; forming an element on the main surface of the upperwafer; forming a second trench within a region surrounded by the throughisolation portion on the main surface of the upper wafer, and thenforming a through interconnect portion electrically connected to asemiconductor circuit unit of another wafer of the plurality of wafersby burying a conductive film in the second trench; and exposing parts ofthe through isolation portion and the through interconnect portion froman undersurface of the upper wafer, a step of forming a lower wafer ofthe plurality of wafers comprising the steps of: forming an elementconfiguring the semiconductor circuit unit on a main surface of thelower wafer; and forming a bump on the main surface of the lower wafer,the bump being electrically connected to the semiconductor circuit unitof the lower wafer, and a step of electrically connecting thesemiconductor circuit units of the plurality of wafers by jointing thethrough interconnect portion exposed from the undersurface of the upperwafer of the plurality of wafers and the bump on the main surface of thelower wafer of the plurality of wafers, with the through interconnectportion and the bump being in contact with each other.
 9. Thesemiconductor device manufacturing method according to claim 8, whereinthe step of exposing parts of the through isolation portion and thethrough interconnect portion from the undersurface of the upper wafercomprises a step of making the upper wafer thinner to an extent not toreach to the through isolation portion and the through interconnectportion from an undersurface of the upper wafer, and then etching fromthe undersurface of the upper wafer until parts of the through isolationportion and the through interconnect portion are exposed.
 10. Thesemiconductor device manufacturing method according to claim 9, whereinthe step of making the wafer thinner to the extent not to reach thethrough isolation portion and the through interconnect portion isperformed through either one of grinding, polishing, and both ofgrinding and polishing.
 11. The semiconductor device manufacturingmethod according to claim 6, wherein the step of forming the throughisolation portion includes a step of forming an insulating film in thefirst trench through thermal oxidation, and the element is formed afterthe through isolation portion is formed on the main surface of the upperwafer.
 12. The semiconductor device manufacturing method according toclaim 6, further comprising: a step of forming the element on the mainsurface of the upper wafer and then depositing a second insulating filmon the main surface of the upper wafer so as to cover the element; astep of forming the second trench extending from an upper surface of thesecond insulating film to a position within a thickness of the upperwafer; and a step of burying the conductive film in the second trench toform the through interconnect portion.
 13. The semiconductor devicemanufacturing method according to claim 6, wherein the conductive filmis made of metal.